Thin film forming device

ABSTRACT

A physical vapor deposition device having a delivery roller for delivering a substrate, a rotatory drum upon which a magnetic recording layer is formed on the substrate and a wind-up roller which winds up said substrate. The device also has a heating source ahead of the rotatory drum and one or more conveying rollers, wherein one of the conveying rollers is an expander roller which is provided between the delivery roller and the rotatory drum. A thin film forming device uses the expander roller and also has a delivery roller, at least one conveying roller and a wind-up roller.

This application is a continuation of application Ser. No. 463,555,filed Jan. 11, 1990 now abandoned, which is a division of applicationSer. No. 283,904, filed Dec. 13, 1988, now U.S. Pat. No. 4,913,933.

BACKGROUND OF THE INVENTION

This invention relates to a method for preparing a magnetic recordingmedium and to a physical vapor deposition device.

In recent years, higher densification of magnetic recording medium suchas tape, disc, etc. has been strongly demanded, and researches anddevelopments of various methods for preparation of medium are underprogress. A method in which a metal thin film is used for the magneticrecording layer of a magnetic recording medium is one of them.

As the method for forming the metal thin film recording layer, the wetprocess method by plating and the physical vapor deposition method suchas vacuum vapor deposition, sputtering, etc. have been studied. In thewet process method, management of the plating bath is cumbersome andtherefore it is not suitable for continuous film formation and alsosevere management is required in disposal of waste liquors, thusinvolving many problems. Therefore, the use of physical vapor depositionprocesses for film formation has become accepted in the art.

As the magnetic recording layer, a vertically magnetized film capable ofaccomplishing high density recording has recently been widely studied.As the vertical magnetized film, a Co type alloy is effective.

In the case of forming a magnetic recording layer of verticallymagnetized film, for obtaining desired magnetic characteristics, it isrequired in most cases to form a film of the magnetic recording layerwhile heating the non-magnetic substrate. However, when a magnetic layeris formed while heating the non-magnetic substrate, wrinkle will begenerated on the substrate.

As the method for preparing a magnetic recording layer on a non-magneticsubstrate according to the vacuum vapor deposition method or thesputtering method, it is most generally practiced to effect filmformation while permitting a polymer substrate to run along a rotarydrum. Whereas, when film formation is effected at a high circumferentialtemperature of the rotary drum, wrinkle will be generated when thepolymer substrate contacts the rotary drum. The cause for generation ofwrinkle may be considered as follows. When the substrate contacts therotary drum, the substrate will be abruptly heated because of hightemperature of the rotary drum, whereby gas liberation from thesubstrate and thermal deformation occur. When a gas is generated fromthe substrate in contact on the rotary drum, gaps are formed between thesubstrate and the drum, which may become the cause for wrinkle. At thesame time, thermal deformation of the substrate is conveyed as such tobecome wrinkle.

Generation of such wrinkle will occur readily when the circumferentialtemperature of the rotary drum is 80° C. or higher and become moremarked as the thickness of the polymer substrate is smaller,particularly 10 μm or less.

In the prior art, for prevention of generation of wrinkle, there haveused the method in which a nip roller 9 is provided as shown in FIG. 5or the method in which the substrate is heated with a lamp 11 on apre-heating roller 10. However, these methods proved to be insufficientby the investigation by the present inventors.

The nip roller 9 is intended to prevent generation of wrinkle bypressing the substrate 1, but when the temperature of the rotary drum 2is high, generation of wrinkle cannot be prevented by pressing of thesubstrate 1 and the wrinkle is pressed under the nip roller 9 to becomefolded wrinkle.

In the case of the pre-heating roller 10, when the temperature of therotary drum 2 becomes higher, the temperature of the pre-heating roller10 must be also made higher, consequently resulting in formation ofwrinkle on the pre-heating roller 10.

SUMMARY OF THE INVENTION

The present invention solves the problems as described above and itsobject is to provide a method for preparing a good magnetic recordingmedium free from wrinkle.

According to one aspect of the present invention, there is provided apreparation method of the present invention comprising delivering asubstrate from a delivery roller, passing the substrate through one or aplurality of conveying rollers and forming a magnetic recording layer onthe above substrate by the physical vapor deposition method in thecourse of running along the circumferential surface of a rotary drum,which method is characterized in that the above substrate is heatedbetween the delivery roller and the conveying roller or betweenconveying a roller and another conveying roller, and the conveyingroller through which the above substrate passes after heating is made anexpander roller.

According to another aspect of the present invention, there is provideda physical vapor deposition device of the present invention comprising adelivery roller for delivering a substrate, a rotary drum which permitsthe above substrate delivered from the above delivery roller through oneor a plurality of conveying rollers to run along the circumferentialsurface thereof and a wind-up roller which winds up the above substrateon which a magnetic recording layer is formed during running along thecircumferential surface of the above rotary drum, which device ischaracterized in that a heating source is provided from a deliveryroller and a conveying roller or between a conveying roller and anotherconveying roller, and the conveying roller lying between the aboveheating source and the above rotary drum is made an expander roller.

According to the method of the present invention, by applying heattreatment on a polymer substrate between rollers on the conveyingpathway from the delivery roller to the rotary drum, and making theconveying roller through which the substrate passes after the heattreatment an expander roller, it is possible to remove wrinklesgenerated during formation of a magnetic recording layer by the physicalvapor deposition method on a polymer substrate in the prior art, wherebya magnetic recording medium free from wrinkle can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the physical vapor deposition device forpracticing the preparation method of the present invention.

FIG. 2 is a perspective view showing an embodiment of the expanderroller.

FIG. 3 is a front view of the expander roller shown in FIG. 2.

FIG. 4 is a cross sectional view of the expander roller shown in FIG. 2.

FIG. 5 and FIG. 6 are front views showing the examples of the physicalvapor deposition devices of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, a magnetic recording medium is preparedaccording to the physical vapor deposition method such as vacuum vapordeposition or sputtering.

In FIG. 1, 1 is a polymer substrate, 2 a rotary drum of whichcircumferential temperature is adapted to be settable as desired up to300° C. 3 is a delivery roller, 4 a wind-up roller, 5 and 6 areconveying rollers. 7 is a mask for restricting the incident angle of aflux of vaporized particles, 8 a vaporization source or a sputteringtarget, 11 a lamp for heating, 12 a conveying roller by use of anexpander roller, and 13 a heat-protecting plate optionally provided forprotection against radiation heat from the rotary drum 2. All of theseare housed within a vacuum tank 14.

Now, the substrate 1 is delivered from the delivery roller 3 and, afterhaving passed the conveying roller 5, is pre-heated with the lamp forheating 11 which is the heating source. At the place where pre-heatingis effected with the lamp 11, the substrate 1 is under completely freestate without contact with any roller. The position where the heatingsource 11 is provided may be preferably a position such that, when azone P (the hatched portion in FIG. 1) formed when moving the orthogonalprojection of the heating source onto the substrate in the directionperpendicular to the substrate 1 is considered, neither the conveyingroller 5 nor the expander roller 12 comes within the zone P. Further,the position may be preferably such that both the conveying roller 5 andthe expander roller 12 do not come within the zone formed by expandingthe zone P to 50 mm therearound.

By providing the heating source 11 as described above, no gas will beliberated from the substrate 1, and even when thermal deformation mayoccur on the substrate 1, since the substrate 1 is not in contact withany other matter, no wrinkle will be generated. As the heating source11, a halogen lamp may be preferably used.

The pre-heated substrate 1 reaches the conveying roller 12 by use of anexpander roller. The thermal deformation of the substrate 1 formed bypre-heating is corrected by the expander roller 12.

The expander roller 12, as shown in FIG. 2, is a roller which rotatesunder curved state.

The position of the top point A on the convex side of the curvedexpander roller 12, if it is once adjusted, is adapted to be unmovableeven when the roller 12 may rotate. In other words, the direction inwhich the convex portion of the expander roller is faced will not moveexcept when adjustment. Such state can be obtained by, for example,rotating only the roller 12 without rotation of the curved shaft 15.

The roller 12 should be preferably formed of an elastic material onaccount of its form. As the elastic material, there may be includednatural rubber and synthetic rubbers generally known as "rubber" [e.g.styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber(IR), ethylene-propylene rubber (EPM, EPDM), butyl rubber (IIR),chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), urethanerubber (U), silicone rubber (Si), fluorine rubber (FPM), polysulfiderubber (T), polyether rubber (POR, CHR, CHC, etc.].

By use of a rubber for the roller 12, the substrate 1 heated isdelivered to the rotary drum 2 without being cooled. For this reason,the substrate 1 will not be abruptly heated on the rotary drum 2,whereby generation of wrinkle can be prevented.

On the expander roller 12 constituted as described above, with rotationfrom the top point B on the concave side to the top point A on theconvex side, its surface becomes gradually enlarged. Accordingly, asshown in FIG. 3 and FIG. 4, in the course of reaching the top point A onthe convex side from the top point B on the concave side, the substrate1 begins to contact the roller 12 (in FIG. 3 and FIG. 4, the substrate 1begins to contact the roller 12 on the generating line a), and byadapting the substrate 1 to be departed from the roller 12 on thegenerating line passing the top point A on the convex side, a tensionwill act on the substrate 1 in the width direction, whereby generationof wrinkle can be prevented.

When the substrate is departed from the roller 12 at a position beyondthe top point A on the convex side, a shrinking force will act on thesubstrate 1 and therefore wrinkle will be formed. For this reason, thedirection in which the convex portion of the roller is faced is adjustedso that the substrate 1 may be departed on the generating line passingthe top point A on the convex side of the roller 12.

The extent of curving of the expander roller cannot be unconditionally,and when the length of the expander roller 12 is 200 mm, the top point Aon the convex side should be preferably higher by 1 to 5 mm from the endof the roller 12. The distance of movement of the substrate 1 in contactwith the expander roller 12 may be preferably about 5 to 20 mm. Theexpander roller 12 should have an outer diameter preferably of 50 to 100mm.

In some cases, the substrate 1 may be delivered from the delivery roller3 directly to the expander roller 12 without via the conveying roller.

Also, when a heat-protecting plate 13 is provided between the expanderroller 12 and the rotary drum 2, the expander roller 12 will not beheated with the radiation heat from the rotary drum, preferably.

The substrate 1 after passing through the expander roller 12 reaches therotary drum 2 and runs along the circumferential surface of the rotarydrum 2. The rotary drum 2 can be set at any desired value ofcircumferential temperature up to 300° C.

The substrate 1, in the course of running along the circumferentialsurface of the rotary drum 2, receives a flux of metal particles fromthe vaporization source or sputtering target 8, whereby a magneticrecording layer is formed thereon. The flux of metal particles isrestricted in its incident angle with the mask 7.

The substrate 1 having a metal film formed thereon then passes throughthe conveying roller 6 and is wound up on the wind-up roller 4. Thus, amagnetic recording medium having a magnetic recording layer of a metalis prepared.

The vacuum deposition device and the sputtering device are distinguishedby whether the flux of particles forming the magnetic recording layer isvaporized from a vaporization source or sputtered from a sputteringtarget, and the constitution of the device is substantially the same.

As the material to be used for the magnetic recording layer, a Co typealloy which becomes the vertically magnetized film is preferred. The Cotype alloy takes h.c.p. structure, in which the C-axis direction becomesthe readily magnetizable direction. Specifically, there can be employedCo-Cr alloys, and otherwise Co-V, Co-Mo, Co-W, Co-Cr-Pd, Co-Cr-Mo,Co-Cr-Rh alloys and alloys in which slight amounts of additives areadded to them.

The coercive force Hcl of the magnetic recording layer of the Co typealloy in the vertical direction to the substrate becomes higher as thetemperature during formation of the magnetic recording layer is higher.The temperature of the substrate 1 is equal to the circumferentialtemperature of the rotary drum 2. Coercive force Hcl is practicallyrequired to be at least 400 Oe. For this purpose, the substratetemperature should be preferably made 80° C. or higher in vacuum vapordeposition and 50° C. or higher in sputtering.

As the substrate 1, films of polyethyleneterephthalate, polyimide oraramide, etc. are suitable.

The thickness of the magnetic recording layer may be suitably within therange of 5 to 100 μm, and the thickness of the substrate within therange of 0.05 to 1.0 μm.

On the magnetic recording layer, as the protective layer, a film formedby oxidation of the magnetic recording layer surface, a layer comprisingAl₂ O₃, SiO₂, Co₃ O₄, Co-Cr-O or Co-Ni-O may be also provided. Further,as the lubricating layer, an organic film of a fluorine type resin, anester type oligomer, etc. may be also provided. Between the substrate 1and the magnetic recording layer, an intermediate layer such as a metalfilm of Ti, Bi, Ge, etc. or an amorphous film may be also interposed. Byproviding such intermediate layer, for example, orientation of themagnetic recording layer 2 can be improved. For the purpose of improvedrecording efficiency and increasing reproduction output, a highpermeability magnetic layer may be also provided between the substrate 1and the magnetic recording layer or between the substrate 1 and theabove intermediate layer.

The present invention is described in more detail by referring toExamples.

EXAMPLES

By use of a vacuum deposition device and a sputtering device having aconveying system as shown in FIG. 1, a magnetic recording layer of Co-Cralloy was formed on a polymer substrate.

As the substrate 1, a polyimide film, aramide film and apolyethyleneterephthalate (PET) film all having a width of 80 mm wereused. For polymide film, those with thicknesses of 7.5 μm and 12.5 μmwere employed. For aramide film, those with thicknesses of 6 μm and 12μm were employed. For PET film those with thicknesses of 7 μm and 10 μmwere employed.

On polyimide film and aramide film, a magnetic recording layer of Co-Cralloy was formed to 0.4 μm by the vacuum vapor deposition method atrespective substrate temperatures of 240° C. and 200° C. On PET film wasfirst formed a Permalloy layer to 0.4 μm by the sputtering method atroom temperature, and then a magnetic recording layer of Co-Cr alloy wasformed to 0.2 μm at a substrate temperature of 90° C.

As the heating source 11, a halogen lamp was used, and the halogen lampwas provided at a distance of 2.0 cm apart from the substrate 1. As theexpander roller 12, one having a length of 200 mm and a diameter of 70mm was used. The expander roller 12 was curved with the top point on theconvex side being higher by 2 mm from the end.

Thus, generation of wrinkle on the magnetic recording medium wasexamined when the power of the halogen lamp was varied from 1.0 (W/cm)to 10.5 (W/cm) at intervals of 0.5 (W/cm). The results are describedbelow.

In the PET film of 7 μm, generation of wrinkle could be prevented withinthe range of the power of the halogen lamp from 1.5 to 2.5 (W/cm). Whenthe power of the halogen lamp exceeded 2.5 (W/cm), plastic deformationof the substrate occurred.

In the PET film of 10 μm, generation of wrinkle could be preventedwithin the range of the power of the halogen lamp from 2.0 to 3.0(W/cm). When the power of the halogen lamp exceeded 3.0 (W/cm), plasticdeformation of the substrate occurred.

In the Aramide film of 6 μm, generation of wrinkle could be preventedwithin the range of the power of the halogen lamp from 3.0 to 6.0(W/cm). When the power of the halogen lamp exceeded 6.0 (W/cm), plasticdeformation of the substrate occurred.

In the Aramide film of 12 μm, generation of wrinkle could be preventedwithin the range of the power of the halogen lamp from 4.0 to 6.5(W/cm). When the power of the halogen lamp exceeded 6.5 (W/cm), plasticdeformation of the substrate occurred.

In the polyimide film of 7.5 μm, generation of wrinkle could beprevented within the range of the power of the halogen lamp from 4.0 to7.0 (W/cm). When the power of the halogen lamp exceeded 7.0 (W/cm),plastic deformation of the substrate occurred.

In the polyimide film of 12.5 μm, generation of wrinkle could beprevented within the range of the power of the halogen lamp from 5.0 to8.0 (W/cm). When the power of the halogen lamp exceeded 8.0 (W/cm),plastic deformation of the substrate occurred.

Also, the coercive force in the vertical direction to the magneticrecording layer of the magnetic recording medium prepared was measured.The results are shown below in Table.

    ______________________________________                                        PET             Aramide     Polyimide                                         7 μm    10 μm 6 μm                                                                              12 μm                                                                             7.5 μm                                                                           12.5 μm                            ______________________________________                                        Hc⊥ (Oe)                                                                         750    750      690  710    800   820                                 ______________________________________                                    

What is claimed is:
 1. A physical vapor deposition device, comprising:adelivery roller; a heating source; an expander roller; a rotary drum;and a wind-up roller, wherein said delivery roller delivers a beltsubstrate along a predetermined path sequentially past said heatingsource for heating said belt substrate and over said expander roller andsaid rotary drum at which a magnetic recording layer is formed on saidbelt substrate to said wind-up roller upon which said substrate havingsaid magnetic recording layer is wound up; said physical vapordeposition device further comprising a vapor deposition source locatedadjacent said rotary drum for forming said magnetic recording layer,wherein said expander roller has a length and a round cross-section,said length having an arcuate profile.
 2. A device according to claim 1,wherein said expander roller is formed of a rubber.
 3. A deviceaccording to claim 1, wherein said round cross-section of said expanderroller has a diameter which is constant along said length.
 4. A deviceaccording to claim 3, wherein said diameter is from 50 to 100 mm.
 5. Adevice according to any of claims 1, 3 or 4, wherein said length of saidexpander roller is 200 mm and said arcuate profile is from 1 to 5 mmhigher at a convex portion that at an end of said expander roller.
 6. Adevice according to claim 5, wherein said belt substrate contacts saidexpander roller from 5 to 20 mm along a circumference of said expanderroller.
 7. A device according to claim 1, further comprising a conveyingroller located between said delivery roller and said heating source. 8.A device according to claim 1 or 7, further comprising a conveyingroller located between said rotatory drum and said wind-up roller.
 9. Adevice according to claim 1, wherein said heating source heats said beltsubstrate within a heating zone and wherein said expander roller is notlocated within said heating zone.
 10. A device according to claim 9,wherein said expander roller is not located within 50 mm of said heatingzone.
 11. A thin film forming device for forming a thin film on a beltsubstrate, comprising:a delivery roller; a heating source; an expanderroller; means for forming said thin film; and a wind-up roller, whereinsaid delivery roller delivers said belt substrate along a predeterminedpath past said heating source for heating said belt substrate, over saidexpander roller and past said means for forming said thin film on saidbelt substrate at a film-forming location to said wind-up roller forwinding up said belt substrate upon which said thin film is formed,wherein said expander roller has a length and a round cross-section,said length having an arcuate profile.
 12. A thin film forming deviceaccording to claim 11, wherein the expander roller is formed of arubber.
 13. A device according to claim 11, wherein said roundcross-section of said expander roller has a diameter which is constantalong said length.
 14. A device according to claim 13, wherein saiddiameter is from 50 to 100 mm.
 15. A device according to any of claims11, 13 or 14, wherein said length of said expander roller is 200 mm andsaid arcuate profile is from 1 to 5 mm higher at a convex portion thatat an end of said expander roller.
 16. A device according to claim 15,wherein said belt substrate contacts said expander roller from 5 to 20mm along a circumference of said expander roller.
 17. A device accordingto any of claims 11, 13 or 14, wherein said means for forming said thinfilm comprises a vaporization source.
 18. A device according to any ofclaims 11, 13 or 14, wherein said means for forming said thin filmcomprises a sputtering target.
 19. A device according to claim 11,further comprising a conveying roller located between said deliveryroller and said heating source.
 20. A device according to claim 11 or19, further comprising a conveying roller located between said thin filmforming means and said wind-up roller.
 21. A device according to claim11, wherein said heating source heats said belt substrate within aheating zone and wherein said expander roller is not located within saidheating zone.
 22. A device according to claim 21, wherein said expanderroller is not located within 50 mm of said heating zone.